Helical Synthetic Nanographenes with Atomic Precision.

ConspectusUnderstanding and harnessing the properties of nanoscale molecular entities are considered as new frontiers in basic chemistry. In this regard, synthetic nanographene with atomic precision has attracted much attention recently. For instance, taking advantage of the marvelous bonding capability of carbon, flat, curved, ribbon-type, or cone-shaped nanographenes have been prepared in highly controllable and elegant manner, allowing one to explore fascinating molecular architectures with intriguing optical, electrochemical, and magnetic characteristics. This stands in stark contrast to other carbon-rich nanomaterials, such as graphite oxides or carbon quantum dots, which preclude thorough investigations because of complicate structural defects. Undoubtedly, synthetic nanographene contributes strongly to modern aromatic chemistry and represents a vibrant field that may deliver transforming functional materials crucial for optoelectronics, nanotechnologies, and biomedicine.Nonetheless, in many cases, synthesis and characterization of nanographene compounds are highly demanding. Low solubility, high molecular strain, undesired selectivity, as well as incomplete or excessive C-C bond formation are common impediments, that require formidable efforts to control the molecular geometry, to modulate the edge structure, to achieve accurate doping, or to push the upper size boundary. These endeavors are indispensable for establishing structure-property relationships, and lay down foundation for exploring synthetic nanographenes at a high level of sophistications.In this Account, we summarize our contributions to this field by presenting a series of helical synthetic nanographenes, such as hexapole [7]helicene (H7H), nitrogen-doped H7H, hexapole [9]helicene (H9H), superhelicene, and supertwistacene. This kind of giant synthetic nanographene reaches the size domain of carbon quantum dots, albeit has precise atomic structure. It provides a unique platform to study aromatic chemistry and chirality at the nanoscale. We discuss synthetic methods and point out, in particular, the strengths and pitfalls of Scholl oxidation, which are expected to be valuable for making synthetic nanographenes in general. In addition, we illustrate their exciting electrochemical and photophysical performance, which include, but are not limited to, reversible multielectron redox chemistry, record high panchromatic absorption, impressive photothermal behavior, and extremely strong Cotton effect. These unusual characteristics are convincingly traced back to their three-dimensional conjugated architectures, highlighting the critical roles of π-electron delocalization, heteroatom-doping, substitution, and molecular symmetry in determining nanographenes' properties and functions. Lastly, we put forward our understanding on the challenges and opportunities that lies ahead and hope this Account will inspire ever more ambitious achievements from this attractive area of research.

Catastrophic cascade of failures in interdependent hypergraphs.

The failures of individual agents can significantly impact the functionality of associated groups in interconnected systems. To reveal these impacts, we develop a threshold model to investigate cascading failures in double-layer hypergraphs with interlayer interdependence. We hypothesize that a hyperedge disintegrates when the proportion of failed nodes within it exceeds a threshold. Due to the interdependence between a node and its replica in the other layer, the disintegrations of these hyperedges could trigger a cascade of events, leading to an iterative collapse across these two layers. We find that double-layer hypergraphs undergo abrupt, discontinuous first-order phase transitions during systemic collapse regardless of the specific threshold value. Additionally, the connectivity measured by average cardinality and hyperdegree plays a crucial role in shaping system robustness. A higher average hyperdegree always strengthens system robustness. However, the relationship between system robustness and average cardinality exhibits non-monotonic behaviors. Specifically, both excessively small and large average cardinalities undermine system robustness. Furthermore, a higher threshold value can boost the system's robustness. In summary, our study provides valuable insights into cascading failure dynamics in double-layer hypergraphs and has practical implications for enhancing the robustness of complex interdependent systems across domains.

Double π-Extended Undecabenzo[7]helicene.

This work reports the first double π-extended undecabenzo[7]helicene 1, which is a large chiral nanographene, composed of 65 fused rings and 186 conjugated carbon atoms. The molecular identity of 1 has been confirmed by single crystal X-ray diffraction. A wine coloured solution of 1 in dichloromethane absorbs light from ultraviolet to the near infrared, featuring an extremely large molar absorption coefficient of 844 000 M-1 cm-1 at 573 nm. Optically pure 1 shows a record high electronic circular dichroism intensity in the visible spectral range (|Δϵ|=1375 M-1 cm-1 at 430 nm) known for any discrete polycyclic aromatic hydrocarbon. These unusual photophysical properties of 1 contrast sharply with those of a mono-undecabenzo[7]helicene derivative 2.

Supertwistacene: A Helical Graphene Nanoribbon.

This work describes a synthetic chiral graphene nanoribbon, named supertwistacene 1. It has four superbenzene (HBC) units linearly fused in a helical manner. The structure of 1, 4.3 nm in length, with an end-to-end twist of 117°, was confirmed by single-crystal X-ray diffraction. In contrast to various twistacene compounds and their analogues, 1 has a very stable configuration. It resists thermal isomerization even when being heated at 200 °C for 16 h. Enantiopure 1 obtained by chiral HPLC shows distinct CD signals in a broad spectral range until 600 nm. In addition, two smaller congeners of 1, the trimer 2 and the dimer 3, were also prepared and systematically investigated. Combining theoretical and experimental studies on 1-3 presents a big picture on their (chir)optical and electronic characteristics.

Fusing of Seven HBCs toward a Green Nanographene Propeller.

This work presents a green chiral nanographene propeller (NP), which is built by fusing seven hexabenzocoronenes in a helical arrangement. It contains 258 conjugated carbon atoms and represents the largest three-dimensional conjugated polycyclic aromatic hydrocarbons ever prepared using scalable solution chemistry. Despite its unusual molecular size, single-crystal X-ray structural analysis (resolution 0.9 Å) and baseline chiral resolution are achieved. NP is soluble in various organic solvents and can be fully characterized by common spectroscopic and voltammetric techniques. It has a strong panchromatic absorption from the ultraviolet to the near-infrared (λmax = 659 nm, ε = 179 000 M-1 cm-1). For instance, more than half of the spectral range between 300 and 800 nm witnesses an extinction coefficient larger than 100 000 M-1 cm-1. Moreover, a record-high Cotton effect in the visible spectrum is observed for enantiopure NP, with |Δε| values of 1182 and 1090 M-1 cm-1 at 374 and 405 nm, respectively. These photophysical properties evolve significantly compared to those of the propeller-shaped hexapole [7]helicene.

Hexapole [9]Helicene.

Herein we present the first hexapole [9]helicene (H9H). Co-catalyzed [2+2+2] cyclotrimerization of a dinaphthopyrene (DNP) functionalized alkyne provides the hexaaryl benzene precursor 2, which is transformed into H9H via a dehydrocyclization reaction. Formation of each embedded [9]helicene involves forging of a new C-C bond, which stitches together two [4]helicene subunits of the neighboring DNP blades, reminiscent of the initial method Martin developed for the preparation of [9]helicene in the 1960s. Single-crystal X-ray analysis of both 2 and H9H discloses their extremely distorted and crowded structural features. Chiral resolution, optical and electronic properties of H9H are also presented.

A Nitrogen-Doped Hexapole [7]Helicene versus Its All-Carbon Analogue.

Two synthetic nanographenes (NGs), N-H7H and C-H7H, were prepared. N-H7H is doped with nitrogen, and C-H7H is the all-carbon analogue. Both are hexapole [7]helicenes (H7Hs), and their structures were identified by single-crystal X-ray diffraction. Sharp contrasts in absorption (abs λmax , 683 vs. 593 nm), emission (em λmax , 894 vs. 777 nm), and electrochemical behavior (ox E1 , 0.28 vs. 0.53 V) were observed between N-H7H and C-H7H, and the origin of these differences was rationalized by theoretical calculations. Studies on N-H7H and C-H7H set a clear example to elucidate the remarkable effects of N-doping on the physical properties of NGs.

Synthesis and Characterization of Hexapole [7]Helicene, A Circularly Twisted Chiral Nanographene.

We report the synthesis and characterization of two hexapole [7]helicenes (H7Hs). Single crystal X-ray diffraction unambiguously confirms the molecular structure. H7H absorbs light, with distinct Cotton effect, from ultraviolet to the near-infrared (λmax = 618 nm). Cyclic voltammetry reveals nine reversible redox states, consecutively from -2 to +6. These chiroptical and electronic properties of H7H are inaccessible from helicene's small homologues.

Synthesis and Characterization of Ferrocene Based Hemicages.

We present a series of tripodal ligands L1-3, which fold into hemicages C1-3 by using coordination-driven dynamic combinational chemistry. The identities of these hemicages were characterized using 1H NMR, 1H-1H COSY, DOSY, and ESI-TWIM-MS. Free rotation of the ferrocene structural units in the ligands affords an adaptable directionality, which is essential for the construction of these hemicages. Encapsulation of adamantane by C2 indicates the presence of a well-defined inner cavity as the binding pocket.

Janusarene: A Homoditopic Molecular Host.

A homoditopic molecular host, janusarene, is presented that has two back-to-back compactly arranged nanocavities for guest complexation. The unique two-face structural feature of janusarene allows it to bind and align various guest compounds concurrently, which include spherical pristine fullerene C60 and planar polycyclic aromatic hydrocarbons (PAHs), such as pyrene, perylene, and 9,10-dimethylanthracene. The host-guest interactions were characterized by single-crystal X-ray diffraction. A pairwise encapsulation of the PAH guests by janusarene enables PAH dimers to be obtained that deliver spectroscopic properties distinct from those of PAHs dissolved in solution, or in the bulk state. A monotopic control host was also synthesized and used to characterize the host-guest complexing behavior in solution.

Stability analysis of loess fill slope supported by frame prestressed anchors considering tensile strength cut-off.

In the stability analysis of loess fill slope, the fissure nature of loess is often ignored, which makes the stability calculation of fill slope too conservative. Based on the upper limit theory of plastic limit analysis, the stability analysis model of loess-filled fissured slope supported by frame prestressed anchors was established. Considering the tensile strength cut-off yield property of soil, the stability coefficient of slope was calculated, and the influence of different factors on slope stability was analyzed. The results show that ignoring the fissures in loess will overestimate the stability of the fill slope, and the support structure can significantly improve the stability of the loess-filled fissure slope. The research results of this paper can further enrich the stability analysis theory of loess-filled fissured slope supported by frame prestressed anchors, which is of great significance to guide engineering practice.

Research on the hydraulic support face guard mechanism and coupling characteristic of rib spalling in large mining heights.

In view of the problem of poor coupling adaptability and easy rib spalling of coal wall in large mining height comprehensive mining, based on the effective inhibition effect of face guard mechanism on coal wall spalling, the structural characteristics and bearing capacity of different structural forms of the face guard mechanism are compared and analyzed. According to the surrounding rock adaptability of the face guard mechanism, established a numerical analysis model for rigid-flexible coupling of the face guard mechanism under different spalling forms. In order to accurately simulate the stress state of the protective mechanism, a variable stiffness spring damping system is used to replace the hydraulic cylinder. The load-bearing performance and response characteristics of the face guard mechanism under rib spalling coupling conditions were analyzed by applying uniform normal load and impact load to the face guard. The findings indicated that, the integral-type face guard mechanism has a better effect on suppressing rib spalling. When the face guard mechanism bears the static load of the coal wall, the entire response process of the face guard jack can be divided into three stages: initial support, increasing resistance bearing, constant resistance bearing; both the impact load position and the coupling state of the rib spalling will affect the characteristics of force transmission at the face guard mechanism's hinge point, the hinge point between the extensible canopy and the primary face guard is most sensitive to biased load. The research results can provide reference for optimizing the face guard mechanism of large mining height hydraulic support and improving the reliability of coal wall support.

Influence of Periodic Disturbance Incoming Flow on the Supercavitation Phenomenon.

Previous studies on supercavitation flow have primarily focused on a standing water environment, neglecting the impact of periodic disturbance in a marine environment. Therefore, a series of periodic functions with different frequencies and amplitudes are defined to simulate the periodic disturbance, and a slender projectile is adopted to numerically study the effect of the periodic disturbance on the supercavitation phenomenon in this paper. Research results show that the cavity profile evolves periodically with the periodic disturbance of the external flow field. At the same time, as the frequency and amplitude increase, the minimum cavity shape gradually decreases to the point that the projectile cannot be wholly enveloped, and the maximum cavity profile gradually increases. Furthermore, the relationship between the cavity length (l i ) and the frequency (f) when the cavity cannot envelop the projectile is obtained (l i = -7.381f + 215.384). Meanwhile, the critical frequency range (7.16 ≤ f < 7.96) and amplitude range (1.1 ≤ am < 1.22) of the cavity to envelop the projectile are obtained. The key factors of periodic disturbances on supercavitation flow are revealed in this paper, which provides a theoretical foundation for maintaining supercavitation flow stability in an environment of periodic disturbance flow.

Comparison efficacy and safety of total laparoscopic gastrectomy and laparoscopically assisted total gastrectomy in treatment of gastric cancer.

BACKGROUND: The development of laparoscopic technology has provided a new choice for surgery of gastric cancer (GC), but the advantages and disadvantages of laparoscopic total gastrectomy (LTG) and laparoscopic-assisted total gastrectomy (LATG) in treatment effect and safety are still controversial. The purpose of this study is to compare the efficacy and safety of the two methods in the treatment of GC, and to provide a basis for clinical decision-making. AIM: To compare the efficacy of totally LTG (TLTG) and LATG in the context of radical gastrectomy for GC. Additionally, we investigated the safety and feasibility of the total laparoscopic esophagojejunostomy technique. METHODS: Literature on comparative studies of the above two surgical methods for GC (TLTG group and LATG group) published before September 2022 were searched in the PubMed, Web of Science, Wanfang Database, CNKI, and other Chinese and English databases. In addition, the following search keywords were used: Gastric cancer, total gastrectomy, total laparoscopy, laparoscopy-assisted, esophagojejunal anastomosis, gastric/stomach cancer, total gastrectomy, totally/completely laparoscopic, laparoscopic assisted/laparoscopy assisted/laparoscopically assisted, and esophagojejunostomy/esophagojejunal anastomosis. Review Manager 5.3 software was used for the meta-analysis after two researchers independently screened the literature, extracted the data, and evaluated the risk of bias in the included studies. RESULTS: After layer-by-layer screening, 258 pieces of literature were recovered, and 11 of those pieces were eventually included. This resulted in a sample size of 2421 instances, with 1115 cases falling into the TLTG group and 1306 cases into the LATG group. Age or sex differences between the two groups were not statistically significant, according to the meta-analysis, however the average body mass index of the TLTG group was considerably higher than that of the LATG group (P = 0.01). Compared with those in the LATG group, the incision length in the TLTG group was significantly shorter (P < 0.001), the amount of intraoperative blood loss was significantly lower (P = 0.003), the number of lymph nodes removed was significantly greater (P = 0.04), and the time of first postoperative feeding and postoperative hospitalization were also significantly shorter (P = 0.03 and 0.02, respectively). There were no significant differences in tumor size, length of proximal incisal margin, total operation time, anastomotic time, postoperative pain score, postoperative anal exhaust time, postoperative anastomosis-related complications (including anastomotic fistula, anastomotic stenosis, and anastomotic hemorrhage), or overall postoperative complication rate (P > 0.05). CONCLUSION: TLTG and esophagojejunostomy are safe and feasible. Compared with LATG, TLTG has the advantages of less trauma, less bleeding, easier access to lymph nodes, and faster postoperative recovery, and TLTG is also suitable for obese patients.

Searching for sliding surfaces in multi-level loess slopes based on the brachistochrone.

As a key problem in slope-stability analysis, searching for potential sliding surfaces has attracted the attention of experts and scholars for a long time. However, the commonly used sliding surface curves are only considered in terms of shape approximation and lack physical significance. The search process involved in stability analysis of multi-level slopes is complex and a large amount of calculation is required. In order to solve this problem, this paper proposes a new sliding surface form based on physical interpretation of the brachistochrone, and establishes a search model for the brachistochrone sliding surface of a multi-level loess slope. At the same time, in order to further expand the search range and find a more ideal potential sliding surface curve shape and position with a lower safety factor, we recommend continuing the sliding-surface search after the brachistochrone is improved. We compared the calculation results for the position of the potential sliding surface and the stability safety factor with the corresponding results for an arc sliding surface (in combination with a calculation example) to verify its rationality. The approach offered here not only provides a new choice of sliding surface curve form for slope-stability analysis, but also significantly improves search efficiency for potential sliding surfaces of multi-level loess slopes.

Evaluation of the Protection Effectiveness of Natural Protected Areas on the Qinghai-Tibet Plateau Based on Ecosystem Services.

Evaluating the protection effectiveness of natural protected areas is an important step in successful management. Adopting 330 natural protected areas on the Qinghai-Tibet Plateau as research subjects, the regional dominant ecosystem service function was selected, and various temporal and spatial analysis methods were employed to analyze the evolution characteristics and influencing factors of ecosystem service patterns from 2000 to 2020. Our results indicated that (1) the water conservation function stabilized after fluctuation and decline, the soil conservation function fluctuated upward, and the windbreak and sand fixation function exhibited an increase after a decreasing fluctuation. (2) The protection effectiveness of25 protected areas significantly improved, that of 151 protected areas improved, that of 84 protected areas stabilized, that of 56 protected areas worsened, and that of 14 protected areas significantly worsened. (3) The top three influencing factors in descending order were precipitation change > altitude > mining area density. (4) Remarkable protection results were achieved in national protected areas, established management institutions, earlier established areas (before 2000), and areas exhibiting alow built-up area density (<0.75%) and low mining density (<1%). Our study provides technical support for the construction and management of protected areas and improvement in ecosystem service functions on the Qinghai-Tibet Plateau.

Notable conservation gaps for biodiversity, ecosystem services and climate change adaptation on the Tibetan Plateau, China.

Incorporating biodiversity, ecosystem services (ESs) and climate change adaptation into the conservation targets of protected areas (PAs) is being acknowledged. Targeting conservation actions requires a thorough understanding of the relationship between PAs and these important regions. However, few studies have identified conservation gaps while simultaneously considering these three aspects. Here, we assessed the representativeness of the PAs network for biodiversity, ESs and climate refugia (as a proxy for climate change adaptation ability) on the Tibetan Plateau (TP). Our analysis showed that these priority conservation regions were primarily located in the south and southeast of the TP, while they were impacted by intense human pressure. Most ESs and all types of species richness showed a significant positive correlation. Additionally, a positive correlation between multiple climate refugia and different types of species richness was detected. Representativeness analysis revealed notable conservation gaps for these three aspects in existing PAs, highlighting the urgency of adjusting their distribution and improving their representativeness. By integrating these conservation targets, priority regions for future conservation were further delineated. Taken together, our findings contribute to improving the efficiency of PAs and optimizing conservation planning.

Vibration response difference of caving mechanism under coal rock impact based on mechanical-hydraulic coupling.

Top coal caving in fully mechanized caving mining will cause an irregular impact on the caving mechanism of hydraulic support. The vibration response of the caving mechanism varies under different forms of impact. This response difference is a prerequisite for new coal rock identification technology in intelligent mining. Therefore, this work studies the difference in vibration response of the caving mechanism under different forms of impact. An innovative mechanical-hydraulic coupling system model of the caving mechanism impact by coal rock is established. The metal plate impact test proved the significant difference in vibration response of the caving mechanism under coal rock impact of different materials. Afterward, a more improved mechanical-hydraulic co-simulation model analyzed the difference in the vibration response of the caving mechanism under different rock materials, volumes, velocities and impact positions. The results show that the vibration response is more intense under rock impact than under coal impact. A lower position, a faster velocity and a larger volume correspond to a more noticeable response difference in the caving mechanism. The vibration and fault sensitive areas of the caving mechanism are determined. This study has a reference significance for improving the caving mechanism's structural design and failure prevention. The conclusions provide guidance for a new intelligent coal rock identification technology based on vibration signals.

Impact Response of the Tail Beam Jack Based on Bidirectional Fluid-Structure Coupling Simulation.

In top coal caving mining, the coal rock collapse will cause an irregular impact on the tail beam jack of the caving control mechanism. The severe impact will lead to jack failure. The bidirectional fluid-structure coupling model is built on Fluent and Mechanical software to study the impact response of the tail beam jack. The dynamic flow velocity streamlines, hydraulic pressure distribution, stress field, and strain field of the jack under impact load are extracted. The response characteristics of the jack in the stationary state and motion state are analyzed. The conclusions are as follows: the stress and strain of the rodless cavity are much larger than those of the rod cavity, which is more likely to be damaged. The hydraulic pressure in the jack cavity is in vertical layered distribution. The flow velocity streamlines present spiral shapes. The response degree of the hydraulic pressure signal in the rodless cavity is stronger than that in the rod cavity, and the response degree of the flow velocity signal in the rod cavity is stronger than that in the rodless cavity. The impact response of the jack in the motion state is more sensitive and stronger than that in the stationary state. The coal rock collapse situation can be most effectively identified only by comprehensively analyzing the rodless cavity's pressure signal and the rod cavity's velocity signal. This paper innovatively visualizes the flow velocity streamlines and pressure distribution together. The bidirectional fluid-structure coupling method is innovatively applied to the tail beam jack. The findings of this study can help for better understanding of the tail beam jack's structural design and failure prevention. This study provides a certain research basis for the intelligent coal rock identification technology in mining coal based on jack vibration signals.

SVep1, a temperate phage of human oral commensal Streptococcus vestibularis.

Introduction: Bacteriophages play a vital role in the human oral microbiome, yet their precise impact on bacterial physiology and microbial communities remains relatively understudied due to the limited isolation and characterization of oral phages. To address this gap, the current study aimed to isolate and characterize novel oral phages. Methods: To achieve this, oral bacteria were isolated using a culture-omics method from 30 samples collected from healthy individuals. These bacteria were then cultured in three different types of media under both aerobic and anaerobic conditions. The samples were subsequently subjected to full-length 16S rRNA gene sequencing for analysis. Subsequently, we performed the isolation of lytic and lysogenic phages targeting all these bacteria. Results: In the initial step, a total of 75 bacterial strains were successfully isolated, representing 30 species and 9 genera. Among these strains, Streptococcus was found to have the highest number of species. Using a full-length 16S rRNA gene similarity threshold of 98.65%, 14 potential novel bacterial species were identified. In the subsequent phase, a temperate phage, which specifically targets the human oral commensal bacterium S. vestibularis strain SVE8, was isolated. The genome of S. vestibularis SVE8 consists of a 1.96-megabase chromosome, along with a 43,492-base pair prophage designated as SVep1. Annotation of SVep1 revealed the presence of 62 open reading frames (ORFs), with the majority of them associated with phage functions. However, it is worth noting that no plaque formation was observed in S. vestibularis SVE8 following lytic induction using mitomycin C. Phage particles were successfully isolated from the supernatant of mitomycin C-treated cultures of S. vestibularis SVE8, and examination using transmission electron microscopy confirmed that SVep1 is a siphovirus. Notably, phylogenetic analysis suggested a common ancestral origin between phage SVep1 and the cos-type phages found in S. thermophilus. Discussion: The presence of SVep1 may confer immunity to S. vestibularis against infection by related phages and holds potential for being engineered as a genetic tool to regulate oral microbiome homeostasis and oral diseases.